1. Field of the Invention
The present invention relates to a cell line expressing oncoprotein E6 of a human papillomavirus type 16 variant strain, and a method of screening an anticancer compound of uterine cervical cancer using the same.
2. Description of the Prior Art
Human papillomavirus (HPV) is a main cause of infection of the genital tract and also causes malignant tumors resulting from oral infection in the skin or oral cavity (Zhebe et al., 1997; Chrisofos et al., 2004). Infection of the genital tract caused by HPV is one of the most common diseases transmitted by sexual contact in both males and females all over the world. Recently, it is one of the most frequently appearing diseases (Ho et al., 1998; Jung et al., 2004). Generation of cancer cells appearing in the uterine cervix is caused mostly by HPV and at least about 120 genotypes of HPV have been known to date. Such a lot of genotypes of HPV may be classified into three types, i.e., the high-risk group, the intermediate-risk group and the low-risk group, depending on the risk of tumors caused by the corresponding type of HPV. Particularly, it is reported that HPV 16, 18 and 31 genotypes of the high-risk group are most highly related to uterine cervical cancer and tumor genesis (zur Hausen., 1996; Koutsky et al., 1997; Munoz et al., 2002; Scheurer et al., 2005).
HPV is a subgroup of papovavirus, is a small non-enveloped virus, and has two kinds of proteins participating in host cell infection and cell cycle. One kind of such proteins is a protein that acts in the initial stage of host cell infection and the other is a protein that controls the cell cycle of the virus in the late stage of host cell infection. Among such proteins, E6 protein that acts in the initial stage plays an important role in the duplication of viral genetic materials and tumor genesis in the host cells. Basically, HPV infection is initiated by damages of epithelial cells. Damages of the basal layer of epithelial cells cause the genetic materials of HPV to start the duplication cycle, which is initiated by the interaction between the materials of host cells and the long control region (LCR) positioned at HPV genomes. Such interaction leads the duplication of E6 and E7 protein genes. These proteins are oncoproteins, and perform their functions as tumor proteins by disturbing the growth factor control path of the host cells through the inactivation or decomposition of p53 or pRb, which is a tumor suppressor gene of the host cells, or by controlling the host cell environment so as to facilitate the duplication of viral genetic materials (Jung et al., 2004). It is known to date that HPV16 and 18 classified as the high-risk HPV genotype are inserted into the infected host cell to cause tumors, in which the interaction between E6 oncoprotein and p53, which is a host tumor suppressor factor, causes uterine cervical cancer (Kiyono et al., 1998; zur Hausen., 1999; Furumoto et al., 2002). It is also known that HPV16 and 18 participate in the immortalization of human epithelial cells together with hTERT (human telomerase reverse transcriptase) (Munger & Howley, 2002).
Meanwhile, it is observed through the study about the HIV infection rate in a domestic high-risk female group and about variant strains that the HIV infection rate is 47% in the domestic high-risk female group and the HPV16 genotype is the most predominant type and occupies 35% of the infection (Choi et al. 2003). After the base sequence of the E6 oncogene is analyzed, it is also observed that 68% thereof are variants (Choi et al., 2007). According to many epidemiologic studies, it is known that HPV16 variant strains affect continuous viral infection and uterine dysplasia resulting therefrom (Berumen et al., 2001, del Refugio Gonzales-Losa et al., 2004; Grodzki et al., 2006; Hildesheim et al., 2001; Lee et al., 2008; Londesborough et al., 1996; Picconi et al., 2003; Sathish et al., 2005; Sichero et al., 2007; Villa et al., 2000; Xi et al., 1995, 1997, 2006). However, there is no sufficient study about the mechanism of generation of uterine cervical cancer caused by such variant strains not only in Korea but also in other countries. After the study of HPV16 E6 L83V (Charkrabarti et al., 2004), it is the only reported result that such variant strains cause uterine cervical cancer in a manner different from the reference strain by activating mitogen-activated protein kinase (MAPK). Recently, active studies have been conducted by many research workers.